Modern diesel fuel systems use an electronically controlled distributor injection pump. These injection pumps need a supplemental high capacity feed pump to deliver fuel to the vehicle fuel system. A typical cost effective feed pump to supply the amount of fuel required is an electrically driven roller vane or similar pump. Electrical energy to this pump is usually provided through a Powertrain Control Module (PCM) or Engine Electronic Controller (EEC).
Providing power through the electronic controller permits several advantages. These advantages include emergency shut down of the fuel pump in the event of an accident, using an inertia switch, to prevent fuel spills. Additionally, the fuel pump can be de-energized, if the key is in the on position, without the engine running. This prevents fuel pump overheating, due to absence of fuel flow. This also prevents excessive noise from the fuel pump, battery drain, and allows maximum electrical energy for starting aids, such as glowplugs. Of course, the pump runs continuously while the engine in running under normal operating conditions.
Unfortunately, if the electric pump is stationary, it usually (roller vane type) will not permit fuel to pass. This renders any manual attempt at priming the vehicle fuel system (removing any air in the fuel system) very difficult. The typical production method of removing air is using a dedicated downstream port, to apply a vacuum.
The typical service method (used after a fuel filter change, or accidentally running out of fuel), is to open a downstream port (usually provided at the Fuel Injection Pump or Main Fuel Filter), then run the electric pump, without running the engine, to purge the air from the system.
Because the fuel pump is NOT designed to run continuously with key on, engine off. Additional hardware has been proposed to allow priming of a diesel fuel system. The additional hardware includes dedicated software in a service tool, to be plugged into a diagnostic connector, an additional feed pump jumper wiring harness, or wiring communicating with the engine bay service light, that would permit the pump to run continuously, with the hood (bonnet) open and the key on.
Each of the above scenarios increases cost and reduces reliability of the overall vehicle. Thus, there exists a need to improve diesel fuel system priming.